The present invention relates to a means to distribute a heavy load uniformly to a plurality of wheels that rotate slowly on circular rails, as in a large crane. The uniform distribution of load is accomplished even when the rails are irregular or inclined.
A crane for moving slowly (say 5 m/min) an extremely heavy object such as a bridge girder weighing hundreds or thousands of tons at a building or construction site is usually installed on a slewing frame provided with a plurality of wheels which roll on circular rails.
It is necessary for the crane supported on rails that the wheels be machined to an accurate diameter, the axles be aligned at a uniform height, and the rail surface be very smooth. To achieve this goal, a high degree of machine finish and great rigidity to prevent distortion are required.
Unfortunately, however, this kind of crane is so large that satisfactory precision is not obtained when assembled and installed at job site.
To solve this problem we made an invention of practical value which matured into Japanese Pat. No. 979,333. We further filed a Japanese patent application (Ser. No. 114898/1979) on the improvement of the previous invention which is characterized by that the axles are oscillated so that they are balanced when the wheels meet with irregular parts of rails. It has been found, however, that this improvement has a problem that the wheel sways when the axles are inclined or load bearing capacity decreases sharply even when the axles are inclined only a little if the wheels are attached to the axles with swivel washers to prevent the wheels from swaying.